Arc-back suppression



Dec. 27, 1938. M. M. MoRAcK 2,141,927

ARC-BACK SUPPRESSION Fileld Dec. '51, 1937 Inventor: I Marvin M. MOTack Jog .w/xtmme Patented Dec. 27, 1938 UNITED STATES PATENT OFFICE ARC-BACK SUPPRESSION New York Application December 31, 1937, Serial No. 182,773

7 Claims.

My invention relates to electric valve converting systems and more particularly to such systems provided with means for suppressing reverse arcs within the valves of the apparatus.

It is a well known fact that any of a number of disturbing operating conditions may cause the valves of an electric valve converting apparatus to have reverse arcs or arc-backs. Such reverse arcs, if allowed to persist, may cause serious damage not only to the valves themselves but to the system and other apparatus with which the electric valve converting apparatus is associated. Heretofore, numerous arrangements have been proposed which have had as their object the elimination or suppression of reverse arcs in the valves of electric valve converting systems. In such systems, however, it would be desirable to have in addition to means for suppressing the reverse arcs, some indication as to which valves were subjected to the first arc-back impulse. While separate indicating systems are' well known, it would be highly desirable if a simple system combining the indication together with suppression of the reverse arcs could be obtained with a minimum of apparatus.

It is, therefore, an object of my invention to provide an improved system for indicating and suppressing the reverse arcs occurring in an electric valve converting apparatus.

It is a still further object of my invention to provide an improved system for indicating and. suppressing the reverse arc in an electric valve converting system which will use the minimum of apparatus and which will be simple and reliable in operation.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents a preferred embodiment of my invention and Fig. 2 shows the application of my invention to a different type of electric valve converting apparatus.

Referring to Fig. 1, as illustrated, an electric valve converting apparatus for transferring energy between an alternating current circuit I0 and a direct current circuit II which includes transformer windings I2 and I3 and a plurality of controlled electric valves I4, I5 and I6. The electric valves I4, I5 and I6 may be any of the type well known in the art having an anode, a

cathode and a control electrode within an envelope containing an ionizable medium. For the purposes of illustration, I have shown these valves as being of the type comprising an anode, a cathode and a starting or ignitor electrode. Each of the starting or ignitor electrodes in the valves l4, I5 and I6 are controlled respectively by one of the auxiliary valves I'I, I8 and I9, which valves may be any of the types commonly utilized in the .art. These valves have been illustrated as each comprising an anode, a cathode, a control grid and a suppressor grid. The cathode and suppressor grid of each of these valves are connected to the ignitor or starting electrode of the main valve and the anodes of these valves are connected through a suitable current limiting resistor to the anodes of the main valves. The control grids of the valves I'I, I8 and I9 are each connected through one of the windings of a control transformer 20 through a pair of resistors 2| and 22 to the common cathode connection of the main valves I4, I5 and I6. If desired, as is customary in the art, these control circuits for the grids may also include suitable current limiting resistors and a source of biasing voltage. The primary winding of the control transformer 20 is energized through a suitable phase shifting device 23 which is connected to the alternating current circuit ID.

The general principles of operation of the electric valve converting apparatus for transferring energy between the direct and alternating current circuits will be well understood by those skilled in the art, so that a detailed explanation is not deemed necessary. The alternating current potential supplied to the control transformer 20 through the phase shifting apparatus 23 causes the auxiliary electric valves I'I, I8 and I9 to become conductive in proper sequence and in response to the conductivity of each of these valves the corresponding main valve I4, I5 or I6 is rendered conductive. In the anode-to-cathode circuit of the main valves I4, I5 and I6 there is connected one of a plurality of relays 24, 25 and 26, respectively. The contacts of each of the relays 24, 25 and 26 are arranged to control the energization of one of a plurality of glow discharge devices 21, 28 and 29 respectively. These glow discharge devices have a critical minimum operating potential characteristic and they are connected in series with a common impedance element or resistor 30 and a suitable source of relatively constant potential 3I which potential is greater than the critical potential of the glow discharge devices.

If arc-backs or other abnormal current conditions should occur in any of the main valves [4, l5 or IE its corresponding relay 24, 25 or 26 would close its contacts so as to impress across the corresponding glow discharge device 21, 28 or 29 potential from the source 3i sufiicient to cause the glow discharge device to become conductive. Since these devices are connected through a common impedance 30 only one of the devices will become conductive regardless as to which relay subsequently applies further potential to the other glow discharge devices. Thus the conductive glow discharge device shows in which valve the arc-back or abnormal current condition first occurs.

For the purpose of suppressing the arc-back there is provided an auxiliary valve 32 having an anode, a cathode and a control grid. The anodeto-cathode circuit of the auxiliary valve 32 includes a suitable source of potential 33 and a resistor 22. The grid-to-cathode circuit of the auxiliary valve 32 includes a resistor 30 and a current limiting resistor 34. If necessary this grid-to-ca hode circuit may include a suitable source of negative biasing potential so that when no potential appears across the impedance element or resistor 39 the auxiliary valve 32 will remain nonconductive. Whenever an arc-back occurs and one of the glow discharge devices 21, 28 or 29 becomes conductive current fiows through the impedance or resistor 30 and this produces a resultant potential, which potential is impressed upon the grid-to-cathode circuit of the auxiliary valve 32 thereby rendering it conductive. The conductivity of the auxiliary valve 32 causes a flow of current through the resistor 22 which develops a potential which is negative with respect to the control grid of the auxiliary valves I'l', I8 and 19. This potential ap earing across the resistor 22 maintains each of the valve [1, l8 and l 9 in a nonconductive condition thereby preventing further conductivity of the electric valves l4, l5 and I6 beyond the half cycle in which the arc-back or abnormal current condition occurs. The system thus described therefore indicates the valve in which the abnormal current condition first arose and also operates to render the control system for the main valves ineffective. thereby suppressing the abnormal current condition.

In Fig. 2 there is illustrated an electric valve converting system for transmitting energy between the alternating current circuit 40 and the direct current circuit 4! utilizing a single cathode multi-anode electric valve device 42. This device 42 may be either of the grid controlled or of the uncontrolled type having field members about the anodes thereof. The device 42 comprises an. insulated cathode 43, a metallic tank member 44, a plurality of anodes .5 and anode shields 46 surrounding the anodes. Each of the anode shields 46 is connected through a suitable current limiting resistor 4'1. a suitable positive biasing source 48, and a resistor 49 to the cathode 43 of the device 42. In the instance of the uncontrolled type of electric valve converting system, the positive biasing source 48 under normal operating conditions maintains the anode shields 46 in a conductive condition. Where it is desired to control the conductivity of the anode 45 the cathode-to-grid circuit may include a negative biasing potential and a suitable source of periodic potential for periodically rendering conductive the discharge paths between the anode 45 and the cathode 43. Each of the anodes is connected through one of the relays 50 and 5! to the secondary winding of the transformer 52 which interconnects the direct and alternating current circuits. Contacts of the relays 50 and 5| are connected respectively to control the energization of the pair of glow discharge devices 53 and 54 which are connected through a common impedance 55 to a suitable source of relatively constant potential 56. Upon occurrence of arc-back or abnormal current conditions the relays 50 or 5| will operate to energize the low discharge devices 53 or 54 to indicate in which one of the anode circuits the initial abnormal current condition occurred. An auxiliary discharge device 51 having an anode, a cathode and a control grid is ccnnected to be responsive to the potential developed across the resistor or impedance element whenever one of the glow discharge devices becomes conductive. The grid-to-cathode circuit of the auxiliary discharge device 51 therefore includes a current limiting resistor 58 and an impedance or resistor device 55 which device is common to the circuits of the glow discharge devices 53 and 54. The anode-to-cathode circuit of the auxiliary discharge device 5! includes a suitable source of potential 59, the source of potential 48 and the resistor 49. Whenever one of the glow discharge devices 53 or 54 becomes conductive current flows therethrough causing a resultant potential to appear across the impedance or resistor 55. This resultant potential is impressed upon the control circuit of the auxiliary valve 51 thereby rendering it conductive and causing current to flow between the anode and cathode of the auxiliary discharge device. The anode-cathode current flow of the auxiliary discharge device 51 produces a voltage component across the impedance or resistor 49 which is sufficient to bias the grid 45 negatively with respect to the cathode 43 thereby rendering the electric valve device 42 nonconductive. Thus the arrangement disclosed in Fig. 2 operates in a manner similar to that disclosed in Fig. 1 in that it indicates in which valve circuit the first abnormal disturbance occurred and in that it also renders nonconductive all of the valve paths and in the instance of a grid control rectifier it would ren der inefiective the grid control circuit thereof.

While I have described what I at present consider the preferred embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made in the circuit arrangements and in the instrumentalities employed without departing from my invention and I, therefore, aim in the ap:- pended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electric valve converting system including a plurality of electric valves, a voltage-responsive element for each of said valves and having a critical minimum operating potential characteristic, an impedance element common to all of said voltage-responsive elements, means associated with said valves for applying a constant potential to said voltageresponsive elements upon occurrence of any abnormal current condition in any of said valves, and means responsive to the resultant voltage across said impedance element for rendering non-conductive said valves.

2. In combination, a plurality of electric valves each provided with a control electrode, a control circuit for said electrodes, a source of nega iii) tive bias, a glow-discharge device for each of said valves, a source of constant potential suificient to render conductive said devices, means responsive to a predetermined electrical condition of any one of said valves for applying said potential to one of said devices, and means'responsive to the conductivity of said device for applying said source of bias to said control circuit to render it ineffective.

- 3. In combination, a plurality of electric valves each provided with a control electrode, a control circuit for said electrodes, a glow-discharge device for each of said valves, a source of constant potential sufiicient to render conductive said glow-discharge devices, means responsive to a predetermined electrical condition of any one of said valves for applying said potential to one of said devices, and means responsive to the conductivity of any of said glow-discharge devices for rendering ineffective said control circuit.

4. In combination, a plurality of electric valves each provided With a control electrode, a control circuit for said electrodes, a voltage responsive element for each valve having a predetermined minimum operating potential characteristic, a source of constant potential sufficient to operate said voltage responsive elements, means responsive to a predetermined electrical condition of any one of said valves for applying said potential to one of said voltage-responsive elements, and means responsive to the conductivity of said voltage-responsive element for rendering ineffective said control circuit.

5. In combination, an electric valve converting system including a plurality of controlled electric valves, a control circuit for said valves, a voltage-responsive element having a critical minimum operating potential characteristic for each of said valves, an impedance element common to all of said voltage-responsive elements, a source of potential of a value greater than said critical potential, means associated with said valves for applying said potential to said elements upon occurrence of an abnormal current condition in any of said valves, and means responsive to the resultant voltage across said impedance element for rendering ineffective said valve control circuit.

6. In combination, a plurality of electric valves each provided with a control electrode, a control circuit for said electrodes, a voltage-responsive element for each valve and having a predetermined minimum operating potential character istic, an impedance element common to said first elements, a source of potential of a value greater than said critical potential, means associated with said valves responsive to abnormal current conditions for applying said potential to said elements, and means responsive to the resultant voltage across said impedance element for applying a negative bias to said control circuit, thereby to render non-conductive said valves.

7. In combination, a plurality of electric valves each having a grid electrode, a voltage-responsive element for each of said valves, said elements having a critical minimum operating potential characteristic, a source of potential, an impedance element common to said voltage-responsive elements, means responsive to abnormal current conditions in any of said valves for applying said potential to said elements, a source of negative bias for said valves, and means responsive to the resultant potential across said impedance element for applying said negative bias to said grids.

MARVIN M. MORACK. 

